Metal-coated metal articles and process of making same



Patented Aug. 17,1926.

- UNITED-STATES SPENCER OTIS AND .WILSON T. HERREN, OF BARRINGTON, ILLINOIS, ASSIGNORS TO NATIONAL BOILER WASHING COMPAN CORPORATION OF ILLINOIS.

PATENT OFFICE.

Y OF ILLINOIS, OF CHICAGO, ILLINOIS, A

METAL-COATED METAL ARTICLES AND PROCESS OF MAKING SAME.

No Drawing.

The value of lead as a coating for iron and steel pipe and other articles to protect them against corrosion has long been recognized, but its use for this purpose has been limited by reason ofthe difliculty of securing reliable covering free from pinholes and other imperfections and which will be firmly adherent throughout. Various methods have been proposed to overcome the difficulty but all have so far failed to reliably produce satisfactory coatings. A considerable degree of success has been obtained by first coating the pipe or other ferrous article to be protected with a thin film of tin and then applying the lead coating thereto, preferably by dipping. \Ve have found that greatly improved results are obtained if more or less cadmium be incorporated with the intermediate film of tin. More or less copper may also be included though this is not essential. The most satisfactory method known to us of securing such a mixed film is by means of electro-deposition, preferably from a mixed bath of tin and cadmium salts.

In practice we have employed an electrolytic bath made up as follows:

First a solution was made containing Oz. per gal.

Copper cyanid (cuprous) 3 Sodium cyanid 4 Sodium carbonate 2 To this solution we added the following:

Oz. per gal.

Cadmiumoxid 1% Sodium cyanid 5 Caustic soda A 8 Stannous chlorid 5 The cadmium is, of course, dissolved as a cyanid Preferably anodes of an alloy containing tin, copper and cadmium in approximately the same proportion as that in which these metals are present in the bath asgiven above Application filed November 11, 1925. Serial No. 68,454.

are employed in the electro-deposition of the coating so that the bath may be replenished. A current density of about two amperes per square foot may be employed.

Before electroplating the pipe or other articles to be coated are preferably cleaned in any known or approved manner; we have found it satisfactory to first tumble them and then wash them in hot solution of canstic soda, the strength of which may be about ten per cent. After cleaning the pipe are then electroplated as above described. Next they are washed and after dipping in a fluxing bath which may consist of zinc chlorid are finally coated by dipping in molten lead preferably heated well above its melting temperature.

The addition of cadmium to the tin seems to greatly improve the cementing efliect of the intermediate film and furthermore to greatly retard the effect-of exposure to the atmosphere in case the application of the final coat of lead is for any reason delayed. It appears that the cadmium, which is next to iron in the electromotive series. is particularly valuable not only in protecting the iron, but also in promoting firm adhesion thereto.

The copper may in some cases be omitted, but it has theeffect of increasing the density of the coating. Other metals readily alloying with lead may be substituted for the tin though I have found the latter to be the best metal for the purpose. In the following claims, however, where the word tin is used it is to be understood as including similar metals which alloy readily with lead.

lVe claim:

1. A ferrous metal article coated With lead there being an intermediate film between the coating and article of tin and cadmium.

' 2. A process of coating ferrous articles with lead which consists in first electro-depositing .iereon a film comprising tin and cadmium and then applying a coating of lead.

3.- A process of coating ferrous articles with lead which consists in first eleetro-depositing a film of tin and cadmium thereon from a bath containing cadmium and tin in approximately the proportion of two to three parts of cadmium to five parts of tin and then dipping the articles in molten i0 lead.

4. A ferrous metal article coatedwith lead,- there being an intermediate film between the coating and article of tin, cadmium and copper.

5. A process of coating ferrous articles with lead which consists 1n first electro-depositing thereon a film comprising tin, cadmium and copper and then applying a coating of lead.

SPENCER OTIS. WILSON T. HERREN. 

